Associations between Mycobacterium paratuberculosis sero-status, milk quality parameters, and reproduction in dairy cows.

The objective of this study was to investigate the influence of Mycobocterium avium subsp. paratuberculosis (MAP) sero-status of dairy cows on different milk production variables and reproductive traits. The study was carried out on 40 herds from the region of Galicia (North-West Spain). These herds were randomly selected from a larger group that had taken part in a voluntary paratuberculosis control program since 2005, which involves regular serum sampling of every adult animal to run antibody-ELISA tests. Milk production and reproductive data were obtained from the "Dairy Herd Improvement Program (DHIP) of Galicia". All the gathered data were processed following a linear regression model. Results indicated that there was no significant effect of MAP sero-status on individual milk production variables. However, a significant difference was observed at the calving-to-first-insemination interval, with an average increase of 14 days in positive animals compared to negatives. It has to be taken into consideration that the paratuberculosis status was only defined by the serological status. Since para tb-infected animals may have antbodies or may not, para tb-positive animals can also be included in the sero-negative group of animals, which may bias the results.

Evaluation of long-term antibody responses to two inactivated bovine viral diarrhoea virus (BVDV) vaccines.

The aim of the present study was to determine the serological response of heifers after vaccination with two inactivated bovine viral diarrhoea virus (BVDV) vaccines by means of various ELISA tests. Three dairy farms were selected from the Galicia region of Spain. In each herd, a batch of heifers to be vaccinated for the first time was selected and followed for 15 months. Heifers from farm 1 (n=25) were vaccinated with Vaccine A, whereas heifers from farm 2 (n=16) were vaccinated with Vaccine B. Heifers from farm 3 (n=17), where no BVDV vaccines were used, acted as controls. Blood samples were analyzed periodically for BVDV antibodies, using five commercial ELISAs, based on BVDV p80 antigen or whole virus. At the end of the study, none of the animals vaccinated with Vaccine A seroconverted according to p80 antibody status, whereas up to 80% tested positive by ELISA against whole virus antigen. For the animals vaccinated with Vaccine B, 2/16 animals seroconverted according to p80 antibody ELISAs, whereas all had seroconverted according to the ELISA against whole virus antigen. In most cases, based on the use of ELISAs to detect specific antibodies against the p80 protein, at 15 months post-vaccination with inactivated BVDV vaccines the responses did not seem to interfere with detection of antibody to BVDV infection. However, the finding of a small proportion of vaccinated animals seropositive against BVDV p80 antigen suggests that antibodies that interfere with diagnosis of BVDV infection within the herd could exist, even when using p80 ELISAs.

Bovine viral diarrhea virus: correlation between herd seroprevalence and bulk tank milk antibody levels using 4 commercial immunoassays.

The aim of the present study was to establish a relationship between the results obtained using the enzyme-linked immunosorbent assay (ELISA) technique for antibodies in blood serum and milk at herd level. For this purpose, 325 samples of bulk tank milk were analyzed with 4 antibody ELISAs from dairy herds with a prevalence of seropositive animals; seroprevalence was also evaluated. Data were arranged to analyze the sensitivity of the bulk tank milk test to detect herds with high risk of active infection (>65% seroprevalence) and the specificity to detect those with very few (<5%) or no (0%) seropositive animals, respectively. The sensitivity values ranged from 0.92 to 0.70 and the specificity from 0.83 to 0.54 to detect free herds (0% seroprevalence) and from 0.88 to 0.77 to detect herds with <5% of seropositive animals. In a quantitative approach, Pearson correlation coefficients, reported as a measure of linear association between herd seroprevalence and transformed optical density values recorded in bulk tank milk, ranged from 0.71 to 0.86. According to these results, the 4 antibody ELISAs would be valid tests for carrying out a herd classification program using milk samples.